A Green Amphoteric Surfactant Derived From <scp> <i>Rapeseed</i> </scp> Oil for Enhanced Oil Recovery From Carbonate Acidic Oil Reservoirs

ABSTRACT Surfactants with both positive and negative functional groups (amphoteric or zwitterionic) are particularly advantageous in acidic oil reservoirs because they remain stable under harsh chemical conditions, tolerate acidic environments and hard water, and are capable of dramatically lowering the interfacial tension (IFT). Sustainability is also crucial, so this study focuses on an amphoteric surfactant derived from rapeseed oil. Synthesized via a conventional three‐step method from vegetable oil, the surfactant's chemical structure, functional groups, thermal stability, and micellar behavior were thoroughly characterized. To evaluate its efficiency in enhancing oil production, the surfactant was tested for its interfacial performance using IFT and contact angle analyses. Its emulsifying over time was also examined. Additionally, its impact on oil displacement was measured by injecting the solution into carbonate cores containing acidic crude oil. At a concentration of 400 ppm and under optimal salinity, the surfactant lowered IFT to around 0.057 mN/m and sustained this value for nearly a month. Contact angle measurements showed rock wettability alteration, reaching an angle of approximately 60°. The oil‐in‐water emulsion remained stable without phase separation for 20 days, with separation beginning gradually thereafter and nearly completing by day 40. Flooding experiments demonstrated the surfactant's effectiveness, achieving an additional oil recovery of approximately 17% following injection at the optimal concentration and salinity. These findings highlight the rapeseed ‐oil‐based amphoteric surfactant as a promising, eco‐friendly agent for improving oil recovery in acidic carbonate reservoirs.